G protein receptor

G protein-coupled receptors (GPCRs), also known as seven transmembrane domain receptors, 7TM receptors, heptahelical receptors, and G protein-linked receptors (GPLR), comprise a large protein family of transmembrane receptors that sense molecules outside the cell and activate inside signal transduction pathways and, ultimately, cellular responses. G protein-coupled receptors are found only in eukaryotes, including yeast, plants, choanoflagellates, and animals. The ligands that bind and activate these receptors include light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters, and vary in size from small molecules to peptides to large proteins. G protein-coupled receptors are involved in many diseases, but are also the target of around half of all modern medicinal drugs
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These proteins receive chemical signals from outside the cell and pass the signal into the cell, so that the cell can respond to the signal. The structures of the endogenous ligands for GPCRs are exceptionally diverse. They include biogenic amines such as norephnephrine and serotonine, peptides, glycoproteins, lipids, nucleotides, ions, and proteases. The sensation of exogenous stimuli, such as light, odors, and taste, is also mediated by this class of receptors. Activation of the receptor causes an effector inside the cell to produce a second signal chemical, which eventually triggers the cell to react to the original external chemical signal.
A ligand, in this case Norepinepherine (NE), binds to the receptor and induces a conformational change. This conformational change activates the a/b complex. The complex is bound to GDP while it is inactive. GTP replaces GDP, thus activating the Alpha subunit. The activated Alpha subunit undergoes a conformational change and activates Adenylate Cyclase. Once the Adenylate Cyclase is activated, it is then able to convert ATP. The products of ATP conversion are c-AMP and two phosphate molecules. c-AMP is a second messenger used in many processes required for cell survival and growth.

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